Recently, portable terminal devices are used in various business situations (for example, distributors' ordering and product inspection, electricity/gas meter reading, and remote inquiry of stock information). For offline business operations, various business data (for example various business-related document forms, sales report documents, publication materials, and presentation materials) may be stored in portable terminal devices. Such business data is better to remain protected even if a portable terminal device is lost.
From the viewpoint of security, conventionally, applications of portable terminal devices are developed exclusively for predetermined software execution environments (DOJA (called i-appli) (trademark), BREW (trademark), etc.) on predetermined OSs (Operating System: for example, Symbian OS, LINUX (trademark), etc.), and such applications are also used in business operations. The software execution environments provide very high security. Partly because data is created for each application and partly because applications are prohibited from referring to the data of other applications, the data is surely protected.
As described above, data to be protected is under closed environments which do not allow the data to be accessed from others. Even if a portable terminal device is lost, the portable terminal device does not allow its internal data to be accessed unless authentication succeeds (for example, Japanese Laid-open Patent Publication No. 2003-101521).
In the conventional environments, applications are individually developed according to different types of devices. On the other hand, the recent approaches are to standardize applications, and to produce OSs for portable terminals, like WINDOWS MOBILE (trademark), in open environments with the good use of know-how on PC (Personal Computer). The software execution environments are also shifted so as to provide more compatibility.
However, the OSs for portable terminals in open environments are provided with a file access function, which permits even confidential data to be accessed without authentication. In addition, it may be difficult to disable the file access function in terms of the properties of the OSs in open environments.
Therefore, it is demanded that portable terminals become capable of protecting confidential data from unauthorized accesses which are made with such a file access function.